A planar X-ray detector using an active matrix has been developed as a new generation X-ray diagnostic detector. The planar X-ray detector detects X-ray radiation and outputs a radiograph or a real-time X-ray image as a digital signal.
In general, an X-ray detector has an array substrate serving as a photoelectric conversion substrate that converts the fluorescence into an electric signal, a scintillator layer serving as an X-ray conversion section that is provided on the surface of the array substrate and converts the incident X-ray into the fluorescence, a reflective layer that is provided on the scintillator layer as necessary so as to reflect the fluorescence from the scintillator layer towards the array substrate side, and a moisture-proof structure that is provided on the scintillator layer and the reflective layer for protection from outside air or humidity.
Such a X-ray detector converts X-ray into visible light or fluorescence through the scintillator layer and converts the fluorescence into a signal charge through a photoelectric conversion element such as an amorphous silicon (a-Si) photodiode or charge coupled device (CCD), thereby acquiring an image.
A material of the scintillator layer is, generally, cesium iodide (CsI):sodium (Na), cesium iodide (CsI):thallium (Tl), sodium iodide (NaI), or gadolinium oxide sulfide (Gd2O2S) which are selected depending on usage or required characteristics.
Resolution characteristics can be improved by forming grooves in a scintillator layer by dicing, or by making a pillar structure by stacking materials through a vapor-deposition method.
A reflective layer is formed above the scintillator layer as necessary for the purpose of enhancing fluorescence utilization efficiency to improve sensitivity characteristics. That is, of the fluorescence emitted from the scintillator layer, the fluorescence travelling toward the opposite side to the photoelectric conversion element side is reflected by the reflective layer to increase the fluorescence reaching the photoelectric conversion element side.
For example, as a method for forming the reflective layer, there are known a method that forms a metallic layer having a high fluorescent reflectance, such as a silver alloy and aluminum, on the scintillator layer and a method for applying and forming a light-scattering reflective layer containing a light-scattering material such as TiO2 and a binder resin. A method in which a reflection plate having a metallic surface made of aluminum or the like is not formed on the scintillator layer, but brought into close contact with the scintillator layer to reflect the fluorescence is also put to practical use.
A moisture-proof structure for protection from an outside atmosphere is formed above the scintillator layer and the reflective layer (or reflection plate) so as to prevent characteristic degradation caused by the humidity. Particularly, high moisture-proof performance is required when the CsI:Tl film or the CsI:Na film, which is a material of highly hygroscopic property, is used as the scintillator layer.
As a conventional moisture-proof structure, there are known a structure in which a moisture-proof layer such as an AL foil or the like is adhered and sealed to a substrate at its circumference to ensure moisture-proof performance and a structure in which a moisture-proof layer such as an AL foil or a thin plate is bonded and sealed to a substrate through a surrounding ring structure.
An array substrate constituting a part of the X-ray detector has a structure in which photodiodes each functioning as a photoelectric conversion element, thin-film transistors (TFT) each functioning as a switching element, and a wiring layer connecting the above elements are patterned on a glass substrate, and a protective film is formed on the array substrate for flattering and insulating purposes.
A transparent insulating film is used as the protective film because of the need to transmitting light from a scintillator layer formed on the photoelectric conversion element, and the transparent insulating film is made of an organic resin film, an inorganic film such as SiO, SiN, and SiON, or a laminated film of an organic resin film and an inorganic film.
In the case where a scintillator layer made of CsI is formed on the protective film by a vapor-deposition method, adhesion between the protective film and scintillator layer is of an important factor. Particularly, in the case where a paste material containing a light-scattering material and a binder resin is applied on the scintillator layer followed by drying to form a reflective layer, if the scintillator layer is peeled off from the array substrate due to shrinkage stress of the reflective layer, light scatters due to an air gap between the scintillator layer and array substrate, which may result in occurrence of a serious defect that the resolution is deteriorated.
Embodiments have been made in view of the above point, and an object thereof is to provide a highly reliable radiation detector in which adhesion between an array substrate having thereon photoelectric conversion elements and a scintillator layer is improved configured to make characteristic degradation due to peeling of the scintillator layer difficult to occur, and a method of manufacturing the radiation detector.